Bone and joint infections Flashcards
What is osteomyelitis?
Bone infection
What is septic arthritis?
Joint infection
What is prosthetic joint infection?
Infection of an artificial joint replacement
What bacteria most commonly causes bone infections?
Staphylococcus Aureus
What bacterias commonly cause infections of the bones and joints?
Staph Aureus (e.g. MRSA)
Streptococci
Enteric bacteria (e.g. E. Coli, Salmonella)
Coagulase-negative staphylococci (e.g. Staph Epidermis)
Mycobacterium tuberculosis
What are the risk factors for developing a bone or joint infection?
Trauma, medical procedures, skin ulcers (direct inoculation)
Contagious spread (e.g. from nearby skin or soft tissue infection)
Haematogenous dissemination (e.g. through IV route)
Immunosuppression (e.g. DM, renal failure, sickle cell disease)
What microbial factors need to be taken into account when determining the pathology of infections?
Access + Adherence (ability to reach and stick to site for invasion)
Invasion + Evasion (ability to penetrate barriers and evade immune system)
Multiplication
Resistance (to anti-microbial treatment)
Damage (to host cells)
Trasmission
How does an acute infection develop into chronic osteomyelitis?
- Initial infection localised to cortical region
- Infection progression into sub-periosteal space with lifting of the periosteum
- Diffuse infection with sequestrum (avascular necrotic region) and sinus tract (through which pus can escape)
What is sequestrum?
When an infected bone becomes necrotic
What is biofilm?
Bacteria in an organic matrix on an inert surface
What is involucrum?
New bone formation outside sequestrum
What is cloacae?
When pus from the sequestrum escapes through involucrum via holes
What are discharging sinuses?
When infection and pus from cloacae causes skin necrosis
What are the clinical features of osteomyelitis?
Pain, swelling, redness, warmth (typical of inflammation and therefore easy to misdiagnose)
Loss of function, fever, pathological fractures, discharging sinuses
What are the clinical features of septic arthritis?
Pain, swelling, redness, warmth (typical of inflammation and therefore easy to misdiagnose)
Loss of function, fever, damage to articular surfaces
What are common causes of osteomyelitis?
Traumatic infections (open fractures, penetrating wounds) Operative infections (joint replacements, internal fixation of fractures) Secondary to infections close to bones (e.g. burns, pressure ulcers) Contributing factors (e.g. vascular insufficiency due to diabetes or atherosclerosis)
What investigations should be carried out for suspected bone or joint infections?
FBC + inflammatory markers (e.g. CRP)
Blood cultures (x2)
Skin/ ulcer swabs (e.g. for MRSA)
Imaging (e.g. plain radiographs, CT and MRI)
Joint and bone samples (e.g. joint aspiration, bone biopsy)
When are plain radiographs a useful investigation?
Show late changes well but not early changes (such as periosteal reaction)
When are CT scans useful as an investigation?
Useful for showing bone changes but not as useful for soft tissue changes
When are MRI scans useful as an investigation?
Useful for showing soft tissue changes but not as useful for bone changes
How is joint aspiration carried out?
Can be done on the ward under local anaesthetic
Single sample taken for microscopy, culture and PCR tests
What might you see in joint fluid (that has been aspirated) in a patient with a joint infection?
Fluid may be non-viscous, turbid, purulent or blood-stained
Microscopy may show WBCs, bacteria or crystals
How is a bone biopsy carried out?
Under general anaesthetic (in theatre)
Multiple samples taken for culture, PCR tests and histopathology
How are bone and joint infections treated?
- Manage sepsis
- Obtain samples prior to starting abx (if possible)
- Dependent on type of infection:
Septic arthritis requires joint washout in theatre
Osteomyelitis requires surgery if chronic changes present
Prosthetic joint infections require removal and replacement
What antibiotics are used to treat bone and joint infections?
Empirical antibiotics = IV flucloxacillin + IV Benzylpenicillin
Targeted antibiotics are dependent on cultures and sensitivities
How long should antibiotics be given for in the case of a bone or joint infection?
2-6 weeks IV
Further 4-6 weeks PO
What prevention strategies should be in place to minimise bone and joint infections?
Prompt diagnosis and treatment or predisposing conditions
Strictest possible aseptic conditions for joint replacements
Antibiotics embedded into cement used for prosthetic joints
